The bone-chilling cold that has paralysed a large swath of the United States and caused more than a dozen deaths is easing as an errant Arctic air mass retreats, setting the stage for a warmer weekend.
In Chicago, where the mercury dipped as low as 30 degrees below earlier this week, temperatures of -7C on Friday morning felt positively balmy for some in the nation's third-largest city.
"Today's wonderful because it's not below zero," said Mary Crissie, 47, who said she closed her deli franchise in the Loop, Chicago's downtown financial district, on Wednesday.
"I didn't want to put my employees at risk because of the severe weather," she said. "The Loop was a ghost town."
In an extreme but mostly welcome swing in the weather, forecasters were predicting that this week's deep freeze will be replaced by almost spring-like temperatures by the weekend.
Temperatures from southern New England to the Upper Midwest should reach 10C through the weekend and Monday, forecasters say, after a record-breaking cold snap that stopped mail deliveries in some parts of the Midwest and shuttered schools and businesses.
Meteorologists linked the spell of brutal cold to the polar vortex, a reservoir of icy air that usually swirls over the North Pole.
Shifting air currents caused it to slip down through Canada and into the US Midwest this week.
National Weather Service meteorologist Bryan Jackson said on Friday the core of the vortex was pulling back, though residual icy air was still pushing over to the US Northeast.
Temperatures on Friday afternoon ranged from about -10C to -15C in most of the Midwest and Northeast, according to the weather service.
More than a dozen deaths in several states were linked to the deep freeze since Saturday and the number was expected to climb as authorities identified more victims.
On Friday, police in East Moline, Illinois, 260 km west of Chicago, said the weather may have contributed to the death of a FedEx freight driver whose body was found between two trucks on Thursday outside a company distribution hub.
"The weather is being considered by investigators as a circumstance that may have played a role in the death," East Moline Police Captain Darren Gault said.
Cook County's medical examiner's office said there had been one confirmed cold-related death this week in the Chicago area.
A trauma surgeon at the city's largest public hospital had told Reuters news agency on Thursday there were nine cold-related deaths in the city.
Asked about the discrepancy, a spokeswoman for the hospital said they would defer to the medical examiner's office for a definitive tally.
More than 40 cold-temperature records were broken on Thursday, the coldest morning since the polar vortex moved in late on Tuesday.
The mass of Arctic air had clung to a swath of the United States from Iowa and the Dakotas across the Great Lakes region and into Maine for days.
Amtrak restored rail service to and from Chicago on Friday and the US Postal Services resumed mail delivery in six Midwest states after suspending it for days.
